Scientific investigations on valley glaciers engaged some of the greatest natural philosophers of the nineteenth century. Among these, Louis Agassiz has unique importance for he personifies the transition from the protoscientific period of de Saussure and Scheuchzer to the scientific one of Forbes and his successors. In this brief history I have attempted to connect the achievements of the past 50 years with the aspirations of our predecessors.

The principal objectives of glacial geology over the last 50 years have been to establish and explain the history of ice, and in particular glaciation, on Earth and to understand the origin of the erosional and depositional products of ice. One of its major successes has been to establish the tempo and magnitude of change in the global glacier mass during the late Cenozoic ice age, and to demonstrate Earth orbital forcing of these changes. On the larger time-scale of the whole geological record, there has been steady elucidation of the frequency of ice ages since the first evidence of glaciation in rocks 2700 Ma old.

There has also been considerable progress in identifying the processes of glacial erosion and deposition and systematizing their products. It is now important that glacial geologists and glaciologists attempt to establish ways in which glacier behaviour is related to sedimentary processes, and via the geological product of those processes to relate the dynamics of glaciers in the past to processes in the lithosphere, hydrosphere, and atmosphere.

Over the past 50 years, ideas relating to the physical features and dynamics of ice sheets have evolved materially, primarily due to modern technological advances in the acquisition of basic data. This paper therefore does not review contemporary knowledge but records how our perception of ice sheets has changed with time. Rather than dealing with individual contributions to the understanding of ice sheets, major topics and concepts are considered against a background of earlier ideas and theories.

Both the form and extent of the surface features of ice sheets have been defined more clearly by the relatively recent use of satellite studies (imagery and altimetry). In an analogous way, radio echo-sounding has enabled the accurate calculation of ice thicknesses and the mapping of the sub-ice bedrock contours, and hence estimation of the ice volume. Studies on the dynamics of ice sheets have been enhanced by bore-hole sampling of deep ice and the determination of ice-temperature distributions, coupled with measurements of mass balance and both surface and internal ice movement. Internal deformation of ice sheets, surging, and various flow theories are considered in relation to recent modelling studies. Global geophysics inevitably includes the role of ice sheets, and therefore climatological studies and new atmospheric chemistry data, together with information on the distribution of meteorites on the Antarctic ice sheet, are considered critically.

Modern concepts of the evolution of ice sheets have substantially modified earlier ideas of the glacial geologists and have explained much that had previously mystified them.

The practical motivations for research on sea ice are discussed and an historical outline given of work carried out in the interval 1936-86. Advances in understanding the physical properties of sea ice and atmosphere–ice–ocean energy exchanges are listed. It is shown how these factors, together with an increasing ability to formulate changing ice-thickness distributions, have led to the eventual production of sophisticated models of ice movement having a useful predictive capability.

Our understanding of the basic physics underlying the properties of ice has dramatically changed during the last half century. At the beginning of this period it was known that the water molecules in ice were arranged with tetrahedral hydrogen bonding, and it had just been established that the hydrogens were not crystallographically arranged on these bonds; however, the way in which water molecules could re-orient was unknown and the implications of this for the mechanical properties and hence for glacier flow were unexplored. The suggestion of electrical point defects in ice, the L and D defects of Bjerrum and the ionic defects, pointed the way to an understanding first of the dielectric relaxation and electrical conductivity of ice and then to a possible interaction between these electrical properties and the movement of dislocations, and hence the plastic deformation of ice.

Menwhile, much work was done to study the behaviour of ice under various physical conditions and to establish more rigorous laws for many physical properties of single crystals of ice and of various forms of polycrystalline ice, and much work was done to find the crystallographic structures of the various phases of ice including those already known to exist at high pressures. The intriguing appearance of a cubic form of ice at low temperatures was also investigated together with vitreous ice formed at even lower temperatures.

Many of these properties are of great interest to meteorologists trying to understand cloud physics and the physics of thunderstorm electricity as well as to astronomers thinking about ice in space, comets, the icy satellites of the planets, or even on the planets themselves.

The history of snow-cover research is divided into four distinct periods. Before 1900 there were systematic observations of snow but the tools were just being developed to begin serious research. From 1900 to 1936, many investigations were made because of the practical considerations of snow hydrology and snow avalanches. Individuals began the assessment of snow water equivalent for forecasting run-off and the observation of snow structure and texture. Quantitative and physical investigations quickened after government-sponsored laboratories were established in 1936, the same year as the founding of the International Glaciological Society. From 1936 through the 1960s, many detailed investigations were made into snow's physical properties and behavior. Professional societies organized national and regional meetings, and published the results of snow research. Many more laboratories became involved as knowledge about snow was developed and applied to run-off forecasting and avalanche defense. Snow research surged again during the 1970s with the establishment of a new generation of snow scientists using more advanced theory, computers, and instrumentation. As demands continue for solutions to snow problems with new emphasis on old themes, snow research generates knowledge about snow for a wide variety of applications.

Many of the major advances in glaciology during the past 50 years have followed the development and application of new technology for viewing and measuring various characteristics of ice. Microscopes to study ice crystals, radars to probe the internal structure of large ice masses, mass spectrometers to analyze the atomic composition of ice cores, and satellite sensors to measure the global distribution of ice are some of the tools readily adapted by glaciologists. Today, new tools include microcomputers for automatic data logging, large-memory computers for data processing and numerical modeling, sensitive instruments for ice analysis, and satellite sensors for large-scale ice observations. In the future, continued advances in key technologies will help guide the evolution of science questions considered by glaciologists, expanding our view of ice, its fundamental properties, its interactions within the ice–ocean–land–atmosphere system, and its role in the evolution of our global environment.

The literature reporting scientific and engineering investigations on ice has grown rapidly in the past 50 years, and increased by a factor of at least ten in the past 20 years. A review is presented of advances in engineering for ice problems during this period, including ice formation in rivers, lakes, and oceans; ice forces on structures; bearing capacity of ice covers; and atmospheric icing. The difficulties faced by engineers due to the unique physical and mechanical properties of ice and its normal thermal state are emphasized.

After the end of World War II glaciology entered a new golden age, which has yet to end. The quality of this golden age is comparable to the classic period of the nineteenth century. The International Glaciological Society has been the major catalyst, through its very active and co-operative international membership and its Journal of Glaciology in setting the modern major advances in the science of glacier and ice phenomena in motion and sustaining them.